Likewise, the invention relates to a device for carrying out this method, comprising a coilable tubing coiled on a rotary drum and, possibly, assigned one or more separate drums carrying additional coilable tubing coiled thereon, outer ends of coilable tubings on two drums being interconnectable by means of cooperating threads; and injector which in the position of use is located in a position where the axis thereof coincides with the axis of a blow-out preventer; and wherein the injector has a favourable position and orientation in relation to the rotary drum with the coilable tubing coiled thereon.
In connection with coiled tubing operations generally, e.g. drilling operations, it is known to position and align the tubing coil on the rotary drum such in relation to the through-going passage/axis of the injector that an imaginary extension of said passage/axis passes substantially tangentially in relation to the outer circumference of the tubing coil on the drum. Thus, strains acting on the coilable tubing through bendings and straightenings, causing plastic deformation thereof, are reduced.
Norwegian patent application No. 953587 discloses a method and a device for use in coiled tubing operations. According to the above-mentioned application, the coiling/uncoiling drum for the tubing, in addition to its capability of rotating around the axial symmetry axis thereof, is adapted to pivot gradually about a horizontal axis during the coiling on/off of the coilable tubing, in a direction towards the injector upon uncoiling and in the opposite direction whenever the coilable tubing is in the act of being coiled onto the drum. The tangential course of the imaginary extension of the injector's through-going coilable tubing passage in relation to the outer circumference of the tubing coil on the drum is, thus, maintained at any time, irrespective of the size of the tubing coil diameter.
The above-mentioned features represent technical advantages when carrying out coilable tubing operations, but they have no significant influence on the general course of the coilable tubing within the bore hole, below the blowout preventer.
During drilling, such coilable tubing does not follow a rectilinear course but rather an elongate, substantially helical path within the bore hole, and creates a number of contact points/areas in which the friction between the coilable tubing and the bore hole wall can be substantial. In the outer end portion of the coilable tubing, the bit is disposed at the end of an angular transition piece (a so-called bent housing) having an orientation tool and a drive motor at the immediately upstream side of the transition piece. The helical course of the coilable tubing within the bore hole and the prevailing frictional conditions will, especially in connection with a substantial fed-in coilable tubing length, counteract and, in individual cases, prevent feed-in of further coilable tubing length in the drilling direction.
In order to reduce the friction between the coilable tubing and the layers of the crust of the earth (the formation layers), so that the feeding of the coilable tubing is favoured, simultaneously counteracting that the coilable tubing get stuck within the bore hole due to the tight coilable tubing windings combined with a high friction with regard to the bore hole wall, one proceeds in accordance with the inventions as defined in the claims, respectively by means of a drilling equipment as set forth in the claims.
According to the invention, the coilable tubing is put into rotational movements during its feeding movements, the coiled tubing drum with tubing coiled thereon and the injector being put into rotational movements about an axis extending right angled to the rotational axis of the drum, coinciding with the axis of the through-going passage of the injection.
Thus, the tubing drum with coilable tubing coiled thereon can follow a rotational movement along an annular path while the injector rotates about its own vertical axis.
Alternatively, also the drum with coilable tubing coiled thereon can be put into rotational movements about a vertical symmetry axis passing through the rotational axis thereof.
In one constructively built up embodiment, the rotary drum with coilable tubing coiled thereon and the injector may be mounted on a common, driven turret/rotary table having a vertical rotational axis aligned with the longitudinal central axis of the underlying blowout preventer, the drum being disposed, supported on a frame rack at the circumference of the turret, while the injector is mounted at the center of the turret, so that the axis of its through-going passage for the coilable tubing and the rotational axis of the turret coincides. Drilling fluid is supplied to the coilable tubing through the horizontal hollow core of the drum from a supply hose suspended from the free outer end of a carrying arm projecting from a mast of the rig.
In another embodiment, the drum with coilable tubing coiled thereon and rotary along two axes crossing each other perpendicularly, usually a horizontal axis for the coilable tubing's uncoiling and coiling operations and a vertical axis for allotting the coilable tubing a rotational movement during feeding, may be suspended from the derrick below e.g. a hydraulic rotary motor. The supply of drilling fluid to the coilable tubing may be arranged as in the first embodiment.
A considerable advantage achieved through rotating the coilable tubing during feeding thereof is that the orientation tool which previously served to adjust the angled transition piece with the bit rotationally, now may be deleted. Thus, also the hydraulic hoses needed for turning the angled transition piece can be omitted. Thus, one avoids a separate motor for rotating the angled transition piece with the bit, the angled transition piece being rotated by means of the coilable tubing string, so that the transition piece may be orientated in the correct direction for drilling along a predetermined path. Another considerable advantage is that the reduced friction between coilable tubing and bore hole wall results in that the bit is subjected to a larger weight load, resulting in increased drilling rate as well as horizontal hole length.
Drilling mud to the drilling machine/bit and hydraulic energy for operating the injector, come from pumping aggregates of the plant.
As known, the mast of the rig may be adapted to be pushed to and fro across the bore hole.
The coilable tubing may be jointed to a coiled extension tubing by means of end connections of the thread type, as well as drill collars may be mounted into the string in order to increase the weight on the bit.